Optical sensors of this type are, for example, employed for engine pressure measurements and are e.g. built into standard spark plugs for this purpose. Other types are used in miniaturized nozzle pressure sensors, for example. In such sensors, light is emitted from a first fiber to a membrane. This membrane is located at a variable position, i.e. closer to or farther away from the emitting fiber, depending on the amount of pressure that acts thereonto from the other side. Then, the light is reflected at the membrane. A portion of the reflected light impinges onto the second fiber that guides the light to a measuring device in which this light intensity of the light is measured. Eventually, the position of the membrane with respect to the optical fibers and, thus, the pressure prevailing at the membrane at that time of measurement can be deduced from the light intensity measured.
It is a disadvantage of such systems that a small signal is superposed on a huge offset. Therefore, the smallest disturbances of this offset result in dramatic errors in the pressure signal measured.